Surface depleted nitrided materials

ABSTRACT

GRADED NITRIDED ARTICLES, SURFACE MODIFIED IN ALLOY COMPOSITIONS WHEREIN THE SURFACE ZONE CONSISTS OF NITRIDED ALLOYS CONSISTING ESSENTIALLY OF (A) ONE OR MORE METALS OF THE GROUP COLUMBIUM, TATALUM, AND VANADIUM; (B) TITANIUM; AND (C) ONE OR BOTH METALS OF THE GROUP MOLYBDENUM AND TUNGSTEN, A MINOR PORTION OF THE NITROGEN MAY BE REPLACED BY OXYGEN OR BORON. NITRIDED MATERIALS PREPARED FROM HOMOGENEOUS ALLOYS ARE ALSO INCLUDED. THE MATERIALS ARE CHARACTERIZED BY EXCELLENT WEAR AND ABRASION RESISTANCE.

United States Patent ABSTRACT OF THE DISCLOSURE Graded nitridedarticles, surface modified in alloy compositions wherein the surfaceZone consists of nitrided alloys consisting essentially of (A) one ormore metals of the group columbium, tantalum, and vanadium; (B)titanium; and (C) one or both metals of the group molybdenum andtungsten. A minor portion of the nitrogen may be replaced by oxygen orboron. Nitrided materials prepared from homogeneous alloys are alsoincluded. The materials are characterized by excellent wear and abrasionresistance.

CROSS REFERENCE TO RELATED APPLICATION This application is a division ofour pending application Ser. No. 16,595, filed Mar. 4, 1970, now US.Pat. 3,674,-

574 and which in'turn is a continuation-in-part of our 7 pendingapplication, Ser. No. 755,658, entitled Wear Resistant Materials filedAug. 27, 1968, now US. Pat. 3,549,427.

BACKGROUND OF THE INVENTION In our parent application, SerialNo.755,658, referenced above, we have disclosed and claimed certainnitrided alloys consisting essentially of (a) at least one metal of thegroup columbium, tantalum and vanadium;

(b) titanium; and

(c) at least one metal of the group molybdenum and tungsten Y in certainpercentages by weight and compositional relationships as are therein setforth. Such nitrided materials are characterized by, among others,excellent wear and abrasion resistance and oifer substantial utility ascutting tool materials.

In such parent application, we have noted that the desired alloys to benitrided may be formed as free standing thin sections or clad or byvarious means formed as a coating upon different substrates. Similarly,in such parent application, we have noted that a variety of nitridingtreatments maybe employed to eifectuate the desired results.

In the present application, we wish to elaborate upon the teachings ofsaid parent application. The compositions hereof which are nitrided orotherwise treated are the same as the alloy compositions which aredisclosed in our parent application.

Accordingly, our parent application, Ser. No. 755,658, now US. Pat.3,549,427, in its entirety, is incorporated herein by reference We wouldnote that a counterpart of such parent application has issued as BelgiumPat. 720,398. As will be evident, we herein provide additional featuresto said basic invention and certain improvements thereof.

In our parent application, the temperatures are presented uncorrected.In the present application, temperatures are corrected. We used acorrection factor deterice mined by using a tungsten-rheniumthermocouple in conjunction with the sightings of the optical pyro'metermentioned in the parent case.

Furthermore, we would note that it is well known that titanium can benitrided to form a hard surface layer thereon but such material shows achipping propensity due to brittleness. In the practice of ourinvention, such brittleness is avoided by specific alloying as taughtherein prior to nitriding. Additionally, the alloying elements presentin typical commercially available titanium alloys do not produce thesame improvement and nitrided commercial titanium alloys show chippingsimilar to nitrided titanium.

'Ihe nitriding of titanium-rich alloys, i.e. containing about 90 percenttitanium has been studied previously (for example, see E. Mitchell andP. J. Brotherton, J. Institute of Metals, vol. 93 (1964), p. 381).Others have investigated the nitriding of hafnium-base alloys (F. Holtzet al., US. Air Force Report IR-718-7 (II) (1967); molybdenum alloys(US. Pat. 3,161,949); and

tungsten alloys (D. J. Iden and L. Himmel, Acta Met.,

vol. 17 (1969), p. 1483). The treatment of tantalum and certainunspecified tantalum base alloys with air or nitrogen or oxygen isdisclosed in US. Pat. 2,170,844 and the nitriding of columbium isdiscussed in the paper by R. P. Elliott and S. Komjathy, AIMEMetallurgical Society Conference, vol. 10, 1961, p. 367.

In the present application, we wish to clearly point out thesignificance of alloying surface treatments or coatings or claddingswith the present materials and surface treatments wherein nitriding isemployed as the major constituent along with relatively minor amounts ofoxygen and/or boron.

It should be noted that the alloys of the present invention may beemployed on another metal or alloy as a service coating or cladding andwith the proper substrate selection, a highly ductile and/or essentiallyunreacted substrate can be obtained. For example, columbium or tantalumare much less reactive to nitrogen when used in conjunction with thealloys hereof and tungsten and molybdenum do not form stable nitrides atthe nitriding temperatures employed. Spraying and/or fusing the desiredalloy onto the surface are included in the various coating methodsavailable. A variety of direct deposition methods may be employed oralternate layers could be deposited followed by a diffusion annealingtreatment.

As set out in our parent application in determining Whether or not amaterial falls within the scope thereof, certain test criteria were usedas are set forth therein. More particularly, following nitrided samplepreparation lathe turning tests were run thereon at surface speeds fromto 750 surface feet per minute (s.f.m.) on AISI 4340 steel having ahardness of around Rockwell C, (R,,), 43 to 45. A feed rate of 0.005in./rev. and depth of cut of 0.050 in. were used. A standard negativerake tool holder was employed with a 5 back rake and a 15 side cuttingedge angle. Tool wear was measured after removing a given amount ofmaterial.

The principal criterion in our parent application in determining whetherthe nitrided materials pass or fail and thus whether or not they areincluded or excluded from the scope thereof was the ability to cut 2cubic inch metal removal of the 4340 steel at speeds of both 100 and 750s.f.m.

At 750 s.f.m. our high performance, nitrided materials readily pass theinitial test of 2 cu. in. metal removal in about 1 minute. (We wouldnote that by s.f.m. is meant the linear rate at which the material beingcut passes the cutter.)

In some aspects of the present invention, such test criteria of theparent application are inoperative. This is particularly true of thethin sections and surface zones considered herein. The nitrided alloysare the same but in some instances in thin sections the test criteria ofthe parent case are not met herein. However, the materials still offersubstantial wear and abrasion resistant properties.

In evaluating tools and tool materials, failure is often assumed tooccur When the wearland reaches 0.030 inch. With the materials of thisinvention, we selected a rather severe test-we indicate those which aregood (i.e., pass the test), when at 750 s.f.m. and 2 cu. in. removal,there is a uniform wearland of less than 0.025 in. Furthermore, we wouldnot that although chipping is seen in some compositions upon testing at750 s.f.m. the chipping propensit'y is aggravated at lower speeds andbetter assessed at 100 s.f.m. The latter is one of the reasons forselecting both speeds.

Accordingly, a principal object of our invention is to provide certainnovel articles wherein the surface zone thereof is a nitrided alloyconsisting essentially of: (a) at least one metal of the groupcolumbium, tantalum and vanadium; (b) titanium; and (c) at least onemetal of the group molybdenum and tungsten.

' Another object of our invention is to provide said novel articlesaforesaid wherein up to three percent of the titanium content isreplaced by zirconium.

A further object of our invention is to provide such nitrided articleswherein the nitrogen pickup is at least 0.1 milligram per squarecentimeter of surface area.

Still a further object of our invention is to provide such nitridedarticles wherein up to twenty-five percent of the nitrogen weight pickupis replaced by oxygen and/o boron.

These and other objects, features and advantages of our invention willbecome apparent to those skilled in this art from the following detaileddisclosure thereof.

DESCRIPTION OF THE INVENTION An alloy of the compositionCb-20V-4OTi-10Mo was readily reduced to foil by rolling and coatingsthereof were made on molybdenum by fusing this alloy in argon at atemperature of about 3375 F. for a time of two minutes. The coating wetthe substrate well, did not flow excessively, and did not seriouslyreact with the molybdenum. A specimen with a 22 mil coating was nitridedat 2950 F. for two hours and showed a microhard'ness grading andstructure similar to the nitride material in bulk form. Themicrohardness at a depth of /2, 1, and 2 mils was 2190, 1600, and 1365DPN, respectively. A coating of similar thickness was produced ontungsten by dipping tungsten stock into molten Cb-18Ti-18W alloy.

A 3 mil coating of Cb-20V-40Ti-10Mo was also produced on molybdenum byfusing in argon. This was subsequently nitrided at 225 F. for one-halfhour resulting in a nitrogen weight pickup of 1.6 mg. per sq. cm. Themicrohardness at a depth of /s mil from the surface was 1680 DPN. Thenitriding temperature is sufficiently low that such alloys may be coatedon a variety of substrate materials including ferrous alloys andsuccessfully nitrided to produce a hard surface.

Much thinner coatings are readily produced by similar or otherprocedures. As the reactive alloy coating becomes thinner, the amount ofnitrogen pickup for surface hardem'ng is reduced since the nitriding isconcentrated near the surface. Accordingly, in such thin sections thedepth of hardening is reduced. In relatively thin coatings, the weightpickup of nitrogen may be 0.1 to 1 mg. per sq. cm. or less and inthicker coatings the pickup will be over 1 mg. per sq. cm. of surfacearea.

In our copending, referenced parent application, we have shown that fornoncoated homogeneous alloy stock the amount of nitriding required forequivalent surface hardening is dependent upon sample thickness. As thethickness is decreased, the required nitriding temperature and weightpickup are reduced. We have observed a pronounced effect of specimenthickness, particularly at knife edges where the required nitrogenpickup is greatly reduced. Also, such coated or homogeneous materialsmay be used for a wide variety of applications requiring wear andabrasion resistance Where the requirement for surface hardness or depthof hardening may be less than that required for metal cutting.Accordingly, in thin sections of homogeneous alloy material, similar tothin coatings of the alloys, the weight pickup of nitrogen may be 0.1to1mg.persq.cm. a

Anotheruseful method for utilizing our nitrided materials involvescontrolled evaporation of titanium from the surface of an alloy(detitanizing). By this procedure, an alloy, for example, with 'atitanium content greater than that determined by our compositionallimitations, can be depleted in titanium content to bring the surfacealloy content within our prescribed ranges prior to nitriding. We haveheated various alloys containing-the required metals of our invention invacuo at temperatures below the melting point of the alloy. Titaniumevaporation occurred without any substantial change in geometry. Mostimportantly, this was accomplished without the occurrence of significantamounts of porosity. Electron microprobe analyses confirmed thesignificant changes ,in weight that had been observed. A specimen of Cb-45Ti- IOMo vacuum treated at a pressure of 5X10 torr' at 2850 F. forfour hours showed a. decrease in titanium content and a correspondingincrease in columbium and molybdenum content. The decrease in titaniumcontent extended to a considerable depth and in the outer 2 mils thedecrease was about 10 percent. Other vacuum treatments run at 2950? F.for six hours showed even greater titanium loss. A Cb-45Ti-20W alloyvacuum treated at 2850 F. for four hours lost 33 mg. for a x x ,4: inchspecimen weighing 1.9 gram, and a similar, size sample of Cb-SOTi-ZOWvacuum treated at 2950" F. for 6 hours lost 60 mg.

Similar detitanizing effects were shown for Ta-Ti-Mo alloys whereinsubstantial weight losses of titanium were observed without geometrychanges or the development of vsignificant amounts. of porosity.Ta-40Ti-10Mo, initially 2.4 g., vacuum treated .at 2950 F..for 6 hours.lost 54 mg. for a x x sample. Upon nitriding at 3250* F. for 2hours,'this' material cut at'both 750 and s.f.m. All such 'vacuumtreated materials show high surface hardness. It will, of course, beappreciated that such surface evaporation techniques can be applied toalloys that are already within our prescribed composition ranges toeffect desirable structural and property changes.

The. cutting performance of such Cb-40Ti-10Mo vacuurn treated at 2850 F.for 4-hours prior to nitriding at 3250 F. was better than the same alloywhen nitrided without prior detitanizing. It should be notedthat-annealing per se, that is, annealing under conditions wheresignificant evaporation does not occur, has an efiect on. themicrostructural morphology. Such morphology effects due to annealing,which result in greater regularity of structure may produce improvementsfor certainuses, but the compositionel-effect due to treatment in vacuois of value by itself.

Since our nitrided materials present as ahomogeneous material or as acoated article are in a thermodynamically metastable condition, thoseskilledin the art will realize that a variety of heat treatments,including multiple and sequential treatments, can be used to modify thereaction structure and resultingproperties whether performed as part theover-all nitriding reaction or as separate treatments. Improvement incutting properties has been noted by nitriding at lower temperatures forlonger times and by nitriding at lower temperatures followed bynitriding at higher temperatures. However, the required weight pickupfor cutting at 750 SFM is similar to the amount of-nitriding necessarywith a simple-2-hour nitriding treatment. The treatments have includedtypical nitriding followed by aging at lower temperatures in argon ornitrogen. We have also nitride-d at higher temperatures (and longertimes) that normally would produce some embrittlement and thensubsequently annealed in inert gas or at various partial pressures ofnitrogen as a tempering or drawing operation to improve toughness. Thisduplex treatment results in a greater reaction depth with thehardness-toughness relationship controlled by the tempering temperatureand time.

Such treatments can be employed to modify the properties of our nitridedmaterials to produce various combinations of hardness and toughness. Therequired annealing treatment is dependent upon the material usage, alloycomposition and degree of prior nitriding.

The influence of annealing under various conditions for a variety ofnitrided materials may be seen from the data presented in Table I.

We have also nitrided materials directly in an environment suflicientlylow in nitrogen potential that the effect is noted. Nitriding in flowingA0.l% N produces reduced nitrogen pick-up compared to 100% nitrogen.Another method involves sealing the furnace with a measured amount ofnitrogen and allowing the nitrogen con tent to be reduced duringtreatment as a result of the specimens absorbing the available nitrogen.For example, Cb-30Ti-10Mo was reacted in an atmosphere starting with0.45% N balance argon and ending with 0.03% N A specimen treated in thismanner out well at both 750 and 100 s.f.m. The alloy Cb-8 0Ti-10Mofalling outside our invention, was nitrided in A0.l% N for 2 hours at3050 F. Similar to treating in nitrogen, the result was a thickcontinuous 3 mil nitride surface layer and such material failsimmediately in testing at 750 TABLE I Nitriding Argon All treatmenttreatment Microhardness (DPN) at depth ofcomposition F. Hrs. F. Hrs. 0.5mil 1' mil 2 mils 4 mils 8 mils Cb-17Ii-20W 2 None 2, 570 2, 090 1, 8901, 140 906 Cb-l7Ti-20W 2 3, 450 1 220 1, 017 1, 040 857 Cb-17Ti-20W 2 3,450 l 2, 190 1, 420 1, 250 835 765 Cb-17Ti-20W 2 3, 250 2 3, 060 2, 6002, 570 2, 160 985 Ta-20Ti-l0M0 2 None 2, 060 1, 675 1, 480 1, 110Ta-2OTi-10M0 2 3, 250 1 1, 690 175 1, 250 946 Ta-20Tl-10Mo 3, 550 2 3,250 4 1, 790 1, 160 996 1, 060

Argon=0.1 percent nitrogen atmosphere.

The alloy Cb-l7Ti-20W, nitrided at 3450" F. for 2 hours showssubstantial softening when subsequently annealed in argon for 2 hours atthis same temperature. If the anealing is carried out in an atmosphereof A--0.1% N it may be noted that only a moderate decrease in hardnessoccurs and the material grades uniformly in a manner similar to thenitrided condition. 'If annealed at 3250 F. for 2 hours in argon thematerial hardens significantly. The influence of annealing in argon onreducing the uniform hardness gradient for the nitrided Ta-20Ti-10Moalloy may also be seen from the above data. We have found that nitridedalloys containing higher amounts of tungsten or molybdenum softenreadily when annealed in argon. To control this softening, that is,avoiding the formation of a surface-layer that is too soft to cut thehardened steel at 750 s.f.m., we have found regulation of the nitrogencontent of the atmosphere to be a useful parameter. It should be notedthat the A0.l% N atmospherewill harden unnitrided or moderately nitridedalloys but results in softening when used with the highly nitridedalloys in the examples above. A x X A; inch specimen of Cb-Ti-20Wreacted in nitrogen at 3250 F. for 2 hours, cuts well at 750 s.f.m. Whensubsequently treated in A0.l% N for 2 hours, this material continues tonitride as evidenced by a further 8 mg. pick-up.

A number of our materials have been nitrided and subsequently annealed.Although the nitrided alloy passed our cutting test criteria at 750 and100 s.f.m., improvement was achieved by nitriding at 3250 F. for 2 hoursfollowed by annealing in argon at 3250 F. for one hour. Also, goodcombined performance at-750 and 100 s.f.m. was shown forCb-30Ti-20Wnitrided at 3550 F. for 2 hours and annealed at 3550 F. for 1hour. Annealing at 3250 F. for one hour did not produce any significantimprovement and annealing for 4 hours at 3550 F. resulted in failure incutting at 750 s.f.m. Thus, one should use due care in annealingconditions.

In most of our materials, the hardness (and nitride content) grades andlessens as one moves from the surface inwardly. However, we would notethat in some cases such grading extends from a plateau or from a peakhardnesss slightly below the surface and grades inwardly therefrom. Suchmaterials can be effective cutting tools or abrasion resistant articles.

s.f.m. These various alternate nitriding treatments may be applied tothe materials of our invention whether used as a homogeneous alloy or asa coated or surface modified material. In all of the nitridingtreatments and particularly for those involving reducing nitrogenpotential, the effect of the varying stabilities of the metal nitridesmust be considered since this can also contribute to surfacecompositional effects.

Surface alloying techniques are also useful for the preparation of thealloys to be nitrided to produce the materials of our invention. Cb-10Mowas titanized at 2950 F. for 3 hours in vacuo by holding in a pack offine titanium sponge which causes difiusion of titanium into thesurface. This treatment resulted in a 6 mil titanized layer which uponnitriding for 2 hours at 3250 F. yielded a graded reaction zone similarto Cb-Ti-Mo materials. This contrasts with the 4 mil continuous nitridelayer formed on Cb-lOMo without the prior titanizing treatinent whichexhibits cracking of the continuous nitride ayer.

In the present invention, as in the invention disclosed and claimed inour copending parent application, when one wishes to determine whetheror not the material is useful in the nitrided state for purposes hereofcertain compositional ratios and formulae must be employed in somecases. Such formulae represent linear proportionate amounts based onweight percentages.

A modest mathematical statement is required. In the present disclosureand claims, the following ratios shall have the following meanings:

Ratlo A =m When, in the present alloy systems, more than 1 metal of thegroup columbium, tantalum and vanadium is present the maximum totalcontent, in terms of weight percent of such metals must be equal to orless than the total of I 85(Ratio A)+88(Ratio B)+90(Ratio C) and theminimum content thereof when tungsten and/or molybdenum are present mustbe equal to or greater than the total of [(Ratio A)+(Ratio B)] [(Rati0E)'+ (Ratio D)]+(Ratio 0) Furthermore, when there is more than 1 metalofthe group columbium, tantalum and vanadium present ,the maximum amountof titanium permited in the alloy system is equal to or less than theamount determined by the formula I 45(Ratio A+Ratio C)+35(Ratio B) andthe ratio of the content of such metals to the titanium must be greaterthan the ratio determined by Ratio A+Ratio B+O.66(Ratio c) :1

Additionally, when both tungsten and molybdenum are 1 1 present themaximum amount thereof is determined by the formula 60(Ratio A+RatioC)(Ratio D)+50(Ratio B) (Ratio D)+80(Ratio B) We would further note thatwhen columbium alone is used of Group A metals and both molybdenum andtungsten are present the minium amount of columbium required isdetermined by the formula 10(Ratio E)+20(Ratio D) Microhardness (DPN) Atdepth (mils) 0.5

A strip specimen 72 mils thick was prepared using the same titanizingand nitriding procedures and was subsequently bent 45. Cracking of thehard nitrided'case occured on the tension (outer) side. The adherency ofthe hard nitrided 6 mil zone was shown by the fact that none of itspalled from the Ta-10W substrate which was intact.

Another surface alloying procedure involved the combined titanizing andvanadizing of molybdenum or tungsten. This can be accomplished by vacuumpack treatment since titanium and vanadium have similar vapor pressures.Such treatment of molybdenum or tungsten at 2950 F. for 3 hours yields athinner diffusion zone than that observed for the titanizing of Cb-lSMo.The depth of the diffusion zone was about 1 /2 mil with molybdenum andless with tungsten. After nitriding at 3250 F. for 2 hours themicrohardness of the molybdenum sample was 1000, 605, and 190 DPN at0.5, 1, and 2 mils, respectively.

Use of surface alloying or coating techniques can enhance the utility ofpowder processing of the alloys prior to nitriding in a number of ways.For example, a powder processed alloy of Cb-Mo could be formed and thentitanized or a porous molybdenum or tungsten presintered compact couldbe infiltrated by coating methods, These and other techniques can (1)lower sintering temperatures, (2) enhance filling of pores, and (3)reduce shrinkage as compared to making a homogeneous powder part.

We have modified our nitrided material by combining nitriding withoxidizing or boronizing. However, the amount of reaction with such otherhardening agents must be limited, a majority of the weight pick-up isdue to nitriding, and these are essentially nitrided materials. Thealloys may be preoxidized at a temperature where little reaction wouldoccur with nitrogen alone and then subsequently nitrided. Also, thealloys may be reacted with a combined oxidizing and nitridingenvironment al though the relative oxidizing potential must be low sincefor example in air the alloys will preferentially oxidize rather thannitride. A sample. of Cb-30Ti-2OW was nitrided at 3250 F. for 2 hoursand subsequently boronized at 2650 F. for 4 hours. The structuralfeatures of such a material are very similar to the alloy only nitrided;the hardness grades inwardly-and of the total weight pick-up over is dueto nitriding. A smooth surface layer about 0.4 mil thick forms due tothe boronizing treatment that is harder than the nitrided surface.

For comparison, the Cb-30Ti-20W alloy nitrided at 3250" F. for 2 hoursexhibits a microhardness of 2680 DPN at a distance of 6 mil from thesurface. After the subsequent boronizing treatment, the hardness was4550 DPN at the same depth. This duplex treated material passes our testat 750 and SFM but the chipping propensity is increased. Up to 25% ofthe nitrogen pick-up by weight may be replaced by oxygen and/or boron.

Although the alloys receptive to nitriding can be produced by coating orsurface alloying techniques, many uses involve the forming and machiningof a homogeneous alloy or a coated article. One of the advantages inutility of these materials is our ability to form the metallic alloys bycold or hot working and/or to machine (or hone) to shape in therelatively soft condition prior to final nitriding. Only minimaldistortion occurs during nitriding and replication of the starting shapeand surface finish is excellent. The final surface is reproducible andis controlled by original surface condition, alloy composition, andnitriding treatment. For some applications, the utility would beenhanced by lapping, polishing, or other finishing operations afternitriding. The nitrided surface is quite hard but only a small amount ofmaterial removal is required to produce a highly finished surface.

One of the nitrided elfects that we have noticed is an accentuation ofsharp edges. Similar to the established technology'for aluminum oxideceramic insert tools, we have blunted sharp cutting edges prior tonitriding. This has been accomplished by simple tumbling prior tonitriding or by'finishing subsequent to nitriding. High speed cuttingperformance will not be degraded if such edge preparation is limited.The nitrided material can be used as a mechanically locked insert or itcan be bonded or joined by brazing, for example, to a substrate.

.We have also observed the excellent corrosion resistance of both thealloys and the nitrided alloys in strong acids, and these materialscould efiectively be employed for applications requiring both corrosionand abrasion resistance. Both the alloys and the nitrided alloys possessgood structural strength. Thus, the materials can be employed forapplications involving wear resistance and structural properties(hardness, strength, stiffness, toughness) at room and elevatedtemperatures. Other useful properties of the nitrided materials includegood electrical and thermal conductivity, high melting temperature, andthermal shock resistance.

Theexcellent cutting properties and wear resistance of the nitridedmaterials can be elfectively employed with the other useful propertiesof the alloys and nitrided ma terials to produce a wide range ofproducts. Some of these are: single point cutting tools, multiple pointcutting tools (including rotary burrs, files, routers and saws),

drills, taps, punches, dies for extrusion, drawing, and other formingoperations, armor, gun barrel liners, impeller of fan blades, EDP(Electrical Discharge Machining) electrodes, spinnerets, guides (thread,wire, and other), knives, razor blades, scrapers, slitters, shears,forming rolls, grinding media, pulverizing hammers and rolls, capstans,needles, gages (thread, plug, and ring), bearings and bushings, pivots,nozzles, cylinder liners, tire studs, pump parts, mechanical seals suchas rotary seals and valve components, engine components, brake plates,screens, feed screws, sprockets and chains, specialized electricalcontacts, fluid protection tubes, crucibles, molds and casting dies, anda variety of parts used in corrosionabrasion environments in thepaper-making or petrochemical industries, for example.

It will be understood that various modifications and variations may beaffected without departing from the spirit or scope of the novelconcepts of our invention.

We claim as our invention:

1. Graded, nitrided ternary or higher refractory alloy materialconsisting essentially of: at least one metal selected from each of theGroups A, B, and C wherein Group A consists of columbium, tantalum andvanadium; Group B is titanium and Group C consists of molybdenum andtungsten and wherein:

(a) the nitrogen pick-up ranges from 0.1 to less than 1.0 milligram persquare centimeter of surface area, and the surface of the material isdepleted in titanium to the desired composition;

(b) when only columbium and molybdenum are present with titanium therange for the columbium content is from about 20 percent to 85 percent;

(c) when ,only columbium and tungsten are present with titanium therange for the columbium content is from about 10 percent to 85 percent;

((1) when only columbium, molybdenum and tungsten are present withtitanium the minimum amount of columbium required is determined by theformula 10(Ratio E)+20(Ratio D) and the maximum content of columbium isabout 85 percent;

(e) when only tantalum and molybdenum are present with titanium therange for the tantalum content is from about 25 percent to 88 percent;

(if) when only tantalum and tungsten are present with titanium the rangefor the tantalum content is about 10 percent to 88 percent;

(g) when only tantalum, molybdenum and tungsten are present withtitanium the minimum amount of tantalum required is determined by theformula 10(Ratio E) +25 (Ratio D) and the maximum content of tantalum isabout 88 percent;

(h) when only vanadium and a metal selected from the group consisting ofmolybdenum and tungsten and combinations thereof are present withtitanium the range for the vanadium content is about 15 percent to 90percent;

(i) when more than one metal of the group columbium, tantalum andvanadium are present with only molybdenum and titanium the minimum totalcontent of the metals columbium, tantalum and vanadium must be at leastequal to the amount of 20(Ratio A)+25(Ratio B) +15(Ratio C) (j) whenmore than one metal of the group columbium, tantalum and vanadium arepresent with only tungsten and titanium, the minimum total content ofthe metals columbium, tantalum and vanadium must be at least equal tothe amount of 10(Ratio A)+10(Ratio B)+l5(Ratio C) (k) when more than onemetal of the group columbium, tantalum and vanadium are present with mo-10 lybdenum, tungsten and titanium, the minimum total content of themetals columbium, tantalum and vanadium must be at least equal to theamount of [(Ratio A) (Ratio B)] [10(Ratio E) +25(Ratio D)]+l5(Ratio C)(I) when more than one metal of the group columbium, tantalum andvanadium are present the maximum total content thereof must be equal toor less than (Rati0 A)+88(Ratio B)+90(Ratio C) (m) when titanium ispresent with only columbium and a metal selected from the groupmolybdenum and tungsten and combinations thereof, the titanium contentranges from about 1 percent to 45 percent and the columbium to titaniumratio is greater than 1;

(u) when titanium is present with only tantalum and a metal selectedfrom the group molybdenum and tungsten and combinations thereof, thetitanium content ranges from about 1 percent to 35 percent and thetantalum to titanium ratio is greater than 1;

(0) when titanium is present only with vanadium and a metal selectedfrom the group molybdenum and tungsten and combinations thereof, thetitanium content ranges from about 1 percent to 45 percent and thevanadium to titanium ratio is greater than 0.66;

(p) when titanium is present with more than one metal of the groupcolumbium, tantalum and vanadium and a metal selected from the groupmolybdenum and tungsten and combinations thereof, the maximum content oftitanium must be equal to or less than 45 (Ratio A+Ratio C) +35(Ratio B)and the ratio of the content of the metals columbium, tantalum andvanadium to titanium must be equal to or greater than the ratio of(Ratio A) +(Ratio B) +0.66(Ratio C) :1

and the minimum titanium content is 1 percent;

(q) when only molybdenum, titanium and a metal selected from the groupcolumbium and vanadium and combinations thereof are present, the rangefor molybdenum content is from about 2 percent to 60 percent;

(r) when only molybdenum, titanium and tantalum are present the range ofthe molybdenum content is from about 2 percent to 50 percent;

(s) when only tungsten, titanium and a metal selected from the groupcolumbium, tantalum and vanadium and combinations thereof are presentthe range for tungsten content is from about 2 percent to 80 percent;

(t) when molybdenum, tungsten, titanium and a metal selected from thegroup columbium, tantalum, vanadium and combinations thereof are presentthe maximum total content of molybdenum and tungsten must be equal to orless than 60(Ratio A-l-Ratio C) (Ratio D)+ 50(Ratio B)(Ratio D)+80(RatioE) and the minimum content of molybdenum and tungsten is 2 percent; (u)and wherein in the foregoing (v) said depleted titanium surface contentbeing produced prior to nitriding by treating the refractory alloymaterial in a vacuum at a temperature below the melting point of thealloy for a time suflicient to produce the desired depletion in titaniumcontent and depth of depletion.

2. The material as defined in claim 1 wherein up to 3% of the titaniumcontent is replaced by zirconium.

References Cited UNITED STATES PATENTS 12 12/1964 Lenning et al. 2-75-474 12/1964 Douglass et al. 14834 3/1965 Wlodek et al. 75-174 10/1969Wood 148-31.5 7/1972 Hill et al 1483l.5

OTHER REFERENCES CHARLES N. LOVELL, Primary Examiner Berger et a1 75-17715 48-2 .3

US. Cl. X.R.

